We
present a kinetic-energy density-functional theory and the corresponding
kinetic-energy Kohn–Sham (keKS) scheme on a lattice and show
that, by including more observables explicitly in a density-functional
approach, already simple approximation strategies lead to very accurate
results. Here, we promote the kinetic-energy density to a fundamental
variable alongside the density and show for specific cases (analytically
and numerically) that there is a one-to-one correspondence between
the external pair of on-site potential and site-dependent hopping
and the internal pair of density and kinetic-energy density. On the
basis of this mapping, we establish two unknown effective fields,
the mean-field exchange-correlation potential and the mean-field exchange-correlation
hopping, which force the keKS system to generate the same kinetic-energy
density and density as the fully interacting one. We show, by a decomposition
based on the equations of motions for the density and the kinetic-energy
density, that we can construct simple orbital-dependent functionals
that outperform the corresponding exact-exchange Kohn–Sham
(KS) approximation of standard density-functional theory. We do so
by considering the exact KS and keKS systems and comparing the unknown
correlation contributions as well as by comparing self-consistent
calculations based on the mean-field exchange (for the effective potential)
and a uniform (for the effective hopping) approximation for the keKS
and the exact-exchange approximation for the KS system, respectively.